In a typical wireless radio receiver, an external radio frequency (RF) pre-selection filter is used at the front of the actual integrated radio receiver circuit (RXIC) to filter out harmful out-of-band blocking signals and to alleviate the linearity requirements of the RXIC. With current technologies, pre-selection filter can not be integrated on silicon, because the required quality (Q) factors in the filter can not be realized. In most cases, RF filters are realized either with surface or bulk acoustic wave techniques (SAW/BAW). In present technologies, since the center frequencies of the SAW/BAW filters are fixed, several pre-selection filters are needed in radio receivers for multi-standard or multi-mode applications, increasing the cost and complexity.
One known amplifier design is described in P. Rossi et al, “A Variable Gain RF Front-End, Based on Voltage-Voltage Feedback LNA, for Multistandard Applications”, IEEE J. Solid-State Circuits”, vol. 40, pp. 690-697, March 2005. One known filter design is described in EP 1867042.
In multi-mode radio receivers, multiple RF pre-selection filters, switches, and baluns increase significantly the cost of the radio receiver. In addition, this decreases the integration level of the receiver, and increase the bills-of-material (BOM) and complexity of the printed circuit board (PCB). The cost of the actual RXIC is also increased due to the fact that several RF input pins, which are also usually balanced, are needed. Since the RF pre-selection filter (and the possible switches) has finite loss at its passband, it lowers the tolerable noise figure (NF) of the RXIC.
Harmful out-of-band blocking signals can drive the radio receiver to compression. In other words, due to the nonlinearity in the radio receiver, a large blocking signal can desensitize the receiver or reduce the gain of the small desired signal. In addition, blocking signals can increase the receiver NF.